Black Carbon In Exhaust Pipe

[FJ80HI]

What would cause black carbon buildup at the exit of the exhaust pipe? My 92 FJ80 runs like a kitten but seems it must be running lean. 170K miles and it probably has been a while since changing the O2 sensor. Could that be the problem? I average 11 miles per gallon, if I correct this problem should my mileage increase?
Thanks

 

[flintknapper]

You're running rich if anything. You might clean that area and see how long it takes to re-appear. Lots of reasons for a 'rich' condition and it might only be intermittent. IF you were blowing black 'smoke' or getting a lot of white smoke, that would be different and a cause for concern.

In any case, I'd recommend letting your 'spark plugs', not your exhaust pipe....tell the story.

Let us know what you find.

 

[inkpot]

Do you drive lots of little short trips that never warm the engine up all the way?

 

[FJ80HI]

Thank for replies. Sorry as you corrected she seems to be running rich. I normally drive trips of 15- 20 miles and seeing ambient temps here in Hawaii are 70-85 deg F the engine should warm to good temp quickly. My engine temps are all good. I have removed the cats, but still have the EGR in place. The engine uses no coolant and burns no oil and has plenty of power. I change oil regularly. The spark plugs all looked good last time I changed them and I have new wires. When the engine idles it does smell a little like unburned gasoline. Only the inside of the exhaust pipe has carbon on it, not like the back of the truck is getting covered in soot. I recently found cracks on the rubber intake large diameter hose (one after the MAF) and I replace that. Engine did run better after replacing that hose as it was leaking air badly. If anything you would think that leak would have led to a lean condition. I have three other vehicles that are 15-25 years old and are fuel injected with similar miles (BMW, Mitsubishi, and Xterra) and their exhaust pipes are perfectly clean where the fj80 has a lot of carbon, so curious as to the cause. I cleaned the pipe and then ran the truck for about 50 miles and the pipe had a carbon residue on it, not real bad but still a residue.

 

[baldilocks]

Yours sounds exactly like all three of the 80's I've owned.

 

[FJ80HI]

Yours sounds exactly like all three of the 80's I've owned.

So this is normal? I would think Toyota could improve gas mileage if all the carbon were burned in the cylinder.
Thanks

 

[BILT4ME]

Normal.

 

[scottryana]

Haha you do know that this technology is close to 30 years old? Back then the cost of wideband O2 sensors was cost prohibitive and you were lucky if dyno shops had them. They used a narrow band O2 that is very vague with AFR readings. Yes if you took today's technology and went about retuning the 80 series you likely could get 1-3mpg more than you see now.

So this is normal? I would think Toyota could improve gas mileage if all the carbon were burned in the cylinder.
Thanks